1. Field of the Invention
The present invention relates to a new material, i.e., a multilayer nonwoven tissue, wherein one of the layers comprises a hyaluronic acid derivative.
2. Description of Related Art
Studies aimed at obtaining biomaterials composed of hyaluronic acid esters used as such or in mixtures with other polymers, which provide good skin coverage, have led to the creation of various types of products. Tissues such as the gauzes and films described in U.S. Pat. Nos. 4,851,521 and 4,965,353 have been proposed. Limitations on the use of such products as skin coverings are due to their degree of rigidity, which may vary according to how they are made, and to their poor absorption of fluids, such as those exuding from wounds during tissue repair. By using nonwoven tissue production techniques, it is possible to obtain products which combine flexibility with the capacity to strongly absorb fluids. These characteristics are described in various patents, such as U.S. Pat. No. 5,041,104.
Limitations on the use of products composed of hyaluronic acid derivatives and/or their mixtures, obtained using currently known techniques, can for the most part be attributed to:
(1) the poor mechanical characteristics of the material when wet, due to its tendency to form a gel when it comes into contact with aqueous fluids such as physiological fluids;
(2) the excessive use of expensive materials such as hyaluronic acid derivatives or mixtures thereof with other biocompatible and bioabsorbable polymers, resulting in a high cost of the finished product, despite the fact that the polymer need only be present in the layer directly in contact with the application site; and
(3) excessively high vapour transmission values.
These drawbacks are particularly significant in cases where poor exudate production is present.